The present invention relates to an intravascular stent which is coated with a specific biocompatible composition.
It is known that heparin, phosphorylcholine and certain polymer coatings may decrease the thrombogenicity of coronary stents. However they do not appear to reduce neointimal hyperplasia and in-stent restenosis. A large variety of vasoactive substances can easily be embedded in the polymer network without firm chemical bonds. Consequently they potentially can act as an intramural slow release formulation for vasoactive drugs.
Numerous tubular stent designs are now on the market. Many of them consist of a radially expandable metal network, either in the form of a fine wire mesh, of a corrugated ring structure or of a slotted metal tube wall wherein a recurring pattern of holes are cut (e.g. by laser cuting). The stent wall has a thickness of between 0.08 and 0.20 mm and the metal is preferably stainless steel, tantalum or NITINOL. Stents can also have an expandable tubular metal spring like structure (coil stent). Examples of stent structures are known from e.g. U.S. Pat. Nos. 4,739,762, 4,856,516, 5,133,732, 5,135,536, 5,161,547, 5,158,548, 5,183,085, 5,282,823, from WO 94/17754, from European patent applications Nos. 0282175, 0382014, 0540290, 0621017, 0615769, 0669114, 0662307, 0657147 and from European patent application 0791341 of applicant.
Diamond like amorphous material such as diamond like nano composition (DLN) are known from WO97/40207 and WO98/33948.
The use of DLN as biocompatible coating for medical devices is for example known from U.S. Pat. No. 5,352,493, WO 97/40207 and WO 96/39943. U.S. Pat. No. 5,352,493 and WO96/39943 disclose the application of DLN as biocompatible coating for medical devices such as orthopedic devices. WO 97/40207 describes the application of DLN for coating of hip prostheses. In contrast with the above mentioned applications, the coating of intravascular implants, such as stents must meet more severe requirements. The coating needs not only to meet the requirement to be biocompatible, but has to decrease or even to avoid thrombogenicity and histiolymphocytic inflammatory foreign body reaction. Neointimal hyperplasia has to be avoided since it can result in a narrowing or even in a closing of the blood vessel cavity. The narrowing of the blood vessel cavity after implantation of a stent is known as in-stent restenosis.
It is an object of the present invention to provide an intravascular stent coated with a biocompatible material in order to avoid thrombogenicity, histiolympocytic inflammatory foreign body reaction and neointimal hyperplasia. As a consequence the risk for in-stent restenosis is decreased or avoided.
The object of the invention is met by using a new class of biocompatible materials for coating at least a major part of the wall surface of the stent with a coating thickness of preferably less than 4 xcexcm and most preferably between 0.05 and 3 xcexcm. The material used according to the invention contains a diamond like amorphous material. Since the coating resists repeated deformation, it can be applied to a stent with a radially expandable metal mesh or metal coil structure.
The diamond like amorphous material in the coating is preferably a diamond like nano composition (DLN) comprising interpenetrating networks of a-C:H and a-Si:O. Such coatings and methods to apply them are known i.a. from WO 97/40207, PCT/EP97/01878 and WO98/33948. A representative coating of a-C:H and a-Si:O comprises 30 to 70 at % of C, 20 to 40 at % of H, 5 to 15 at % of Si and 5 to 15% of O. For applying these coatings to stents, the latter are preferably in their expanded state, not only radially but also they are longitudinally (axially) stretched to a certain extent if the mesh or spring structure so permits. This allows a substantially uniform deposition of the biocompatible diamond like material (DLN) using plasma-assisted CVD-processes. The plasma is created from a siloxane precursor. A Si-doped DLC can also be deposited; a silane precursor is then used.